1. Field of the Invention
The present invention relates to semiconductor devices. In particular, the present invention relates to a semiconductor device that includes, in a single package, an insulating element or circuit in addition to a plurality of semiconductor elements, where the insulating element carries out signal transmission between the semiconductor elements
2. Description of the Related Art
Inverters are used in electric vehicles (including hybrid vehicles) and home appliances for example, and these inverters may incorporate a semiconductor device provided with an insulating element or circuit. Specifically, an inverter used for an electric vehicle may include power semiconductors (such as insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field effect transistors (MOSFETs)) in addition to a semiconductor device of the above-mentioned type. Such a semiconductor device includes a control element, an insulating element, and a drive element. The inverter supplies a control signal received from an engine control unit (ECU) to the control element of the semiconductor device. The control element converts the control signal into a pulse width modulation (PWM) control signal and transmits the resulting signal to the drive element via the insulating element. According to the PWM control signal, the drive element switches a plurality of (six, for example) IGBTs with a desired timing. Through the switching of the six IGBTs with a desired timing, direct current (DC) power supplied from an on-vehicle battery is converted into three-phase alternating current (AC) power, which is suitable for the motor driving.
In the semiconductor device, the control element operates at a low source voltage (about 5 volts), while the drive element operates at a high source voltage (about 600 volts or higher). Therefore, a PWM control signal (electric signal) from the control element to the drive element needs to be transmitted via the insulating element. A conventional example of the insulating element is a photocoupler. A photocoupler includes a light emitter, such as a light emitting diode (LED), and a light receiver, such as a phototransistor. An electric signal received at the light emitter is converted into an optical signal by the light emitter, and the resulting optical signal is received by the light receiver and converted back into an electric signal. In this way, the electric signal is transmitted. Unfortunately, a semiconductor device formed by mounting a photocoupler as an insulating element, a control element, and a drive element all within a single package tends to be large. In addition, a photocoupler as mentioned above may not be suitable for high-speed switching of IGBTs due to the delay in conversion between an electric signal and an optical signal, which occurs as the frequency of the electric signal is higher.
In view of the above, more and more semiconductor devices include insulating elements with coupled inductors. An inductor-coupled insulating element transmits an electric signal through inductive coupling of two inductors (coils), rather than via electric connection. Specifically, one of the coils converts an electric signal into a magnetic field, and the other coil converts the magnetic field back into an electric signal. This achieves transmission of the electric signal without electric connection. Unlike photocouplers, inductor-coupled insulating elements are suitable for producing compact semiconductor devices and involve little or no delay in transmission of a high-frequency electric signal, which is an advantageous characteristic for high-speed switching of IGBTs. A semiconductor device disclosed in JP-A-2013-51547 includes a semiconductor element having a send circuit, an inductor-coupled insulating element, and a drive element (gate driver integrated circuit) having a receive circuit within a single package.
However, simply providing a semiconductor device with an insulating element may not be sufficient when two semiconductor elements, such as a control element and a drive element, that receive source voltages of significantly different potentials are mounted in the single package. Such a semiconductor device is required to further improve the dielectric strength. In an example of a small outline package (SOP) type, a semiconductor device preferable to further improve the dielectric strength has a sufficient distance separating the terminals exposed from one side surface of the sealing resin from the terminals exposed from the other side surface, with semiconductor elements including a drive element located in between. To further improve the dielectric strength, it is preferable that the terminals are the only portions of a lead frame that are exposed from the sealing resin. The need to further improve dielectric strength increases with increase in the source voltage supplied to a motor controlled by the inverter.
For example, JP-A-2000-68437 discloses a conventional SOP semiconductor device. In the production of the disclosed semiconductor device, a portion of a lead frame called an island support is used to support to an island portion (die pad), which is a portion for mounting semiconductor elements. The island support extends in a direction perpendicular to the extending direction of the terminals and has one end connected to the island portion and another end connected to the peripheral portion of the lead frame. Once the sealing resin is formed, the island portion is supported by the sealing resin and the support by the island support is no longer necessary. Therefore, the island support is cut off from the lead frame when the semiconductor device is cutoff from the lead frame. As a result, a cut surface of the island support is exposed on the side surface of the sealing resin. Since the cur surface of the island support is part of the lead frame, the semiconductor device having such a structure may fail to meet the need to further improve the dielectric strength.